Our long range goal is to elucidate on a cellular and molecular basis how gonadotropic factors and prostaglandins interact with the ovary to regulate follicular maturation, ovulation and corpus luteum lifespan. Specifically, during the coming 5 years we intend to investigate the regulation of corpus luteum lifespan as it depends on endocrine and cellular factors. We will center our attention to the definition of factors that act alone or in combination to cause formation, activation maintenance and regression of corpora lutea (CL). We shall work on rats and rabbits. Parameters to be determined are: serum and luteal levels of progesterone (P4), 20 alpha-hydroxyprogesterone, estradiol (E2); luteal levels and properties of hormone sensitive adenylyl cyclase, of membrane receptors (hCG, PRL, FSH PGF, 20C), and of cytosolic and nuclear E2 receptors. Regression of CL will be studied both as induced pharmacologically by treatment with hCG or LH, by removal of prolactin (PRL) support or by lateration in steroid hormone support, and as it ocurs "physiologically" at the end of the cycle, at the end of pseudopregnancy (PSP) and at the end of pregnancy. Activation of CL will be explored under various conditions including those arising after ovulation in PSP and pregnant animals. Heavy emphasis will be placed on defining the physiological role of PGF 20 in termination of CL lifespan.